The present invention relates generally to methods and apparatuses for transporting light from a single light source to multiple locations, and more particularly, to a method of and apparatus for transporting light from a single light source to multiple locations using a plurality of light fibers.
Optically transmissive materials, such as glass or polymers, may be used as a light guide to propagate light. A light guide typically includes at least one surface adapted to receive light from a light source and an optically smooth surface for reflecting light propagating through or along the light guide. Common examples of light guides include optical fibers traditionally used in the data communication industry and, more recently, light fibers used for illumination purposes. For example, U.S. Pat. No. 4,422,719 (Orcutt) discloses one such light guide employing light fibers. In this device, at least one end surface of the light fiber is adapted to receive light from a light source, which light propagates axially through or along the fiber. Planar waveguides used in the optical display industry are another example of light guides. In these devices, at least one end of the surface of the waveguide is adapted to receive light from a light source, and light injected into the light guide propagates between the two major surfaces of the light guide.
Multiple light fibers can be bundled together to form a light transport device that accepts light from a single source and emits light in directions that are determined by the orientation of the output ends of the fibers. In many cases, it is desirable that the light emitted by the fiber outputs ends be uniform in color and intensity with respect to one another. Unfortunately, such uniformity can be difficult to achieve because light sources typically used to generate light are inhomogenous across their surfaces. That is, each portion of a given light emitting surface emits light that differs in color and intensity. As a result, when a light source is arranged to direct light into the input ends of a bundled fiber arrangement, the color and intensity of the light received by the individual fibers will depend on the portion of the light source surface from which the light is received. Thus, the color and intensity of light emitted from the bundle will generally vary from fiber to fiber.
To enhance the color and uniformity of light emitted by the combined fiber outputs, a mixing element is sometimes inserted between the light source and the input ends of the bundled fibers. For example, U.S. Pat. No. 5,367,590 (Davenport et al.) discloses a mixing element that is formed from a segmented coupler that includes multiple internal reflective surfaces to achieve some degree of mixing to provide uniform color light. This mixing element requires many reflective surfaces to achieve a high degree of mixing and is thus susceptible to significant optical loss. Moreover, the mixing element is relatively complex in design.
Accordingly, it would be desirable to provide a simple, inexpensive and efficient light transport device requiring a minimum of components so that light received from a common source is distributed among a plurality of fibers with uniform color and intensity.
The present invention solves this problem by fabricating light guides such as light fibers with cross-sectional shapes appropriately selected so when the ends are brought into contact with one another in a light injection surface, they form a continuous plane substantially free of voids and free of non-light-guiding material, such as fiber cladding. As a result, light propagating through fibers in direct contact with one another will be able to propagate from one fiber into another so that the light from all fibers is mixed together. Advantageously, mixing will take place without the need for an additional mixing element that is separate from the light fibers themselves.
In one aspect, the present invention relates to an apparatus for transporting light, which includes multiple fibers each having a contacting end and a non-contacting end. The contacting ends, which are assembled into a bundled region that terminates in a light injection plane, have a prescribed cross-sectional shape prior to contacting one another such that, when brought into contact, adjacent contacting ends have outer edges completely contiguous with one another so that the light injection plane is substantially free of voids while each of the contacting ends maintains its respective prescribed cross-sectional shape. The bundled region is configured so that light propagating in the light fibers undergoes mixing by being coupled from one light fiber to another. Light in each fiber will therefore be mixed, reducing or even eliminating any inhomogeneities in color or intensity that may have initially been present.
In another aspect, the present invention relates to an apparatus of the type described above in which the entire bundled region is substantially free of both voids and non-light guiding material such as a cladding, for example. That is, adjacent fiber cores are in direct contact with one another to facilitate the mixing of light among the fibers.
In yet another aspect, the present invention relates to an apparatus of the type described above in which the bundled region has a length that is sufficient to ensure that light directed from a light source into the light injection plane is substantially uniform in color and/or intensity when being emitted from each of the noncontacting ends of the light guides.
In still another aspect, the present invention relates to an apparatus of the type described above in which at least one of the contacting ends has a noncircular cross-sectional shape, such as a sector or a rectangle.
In yet another aspect, the present invention relates to an apparatus of the type described above in which the apparatus includes N light fibers, where N is an integer greater than or equal to 2. Each of the N light fibers has a cross-sectional shape corresponding to a sector. The N sectors may each extend over an angle of 360/N degrees. Alternatively, at least two of the N sectors have a different angular extent.
In still another aspect, the present invention relates to an apparatus of the type described above in which the plurality of contacting ends have cross-sectional shapes that differ from one another. In this embodiment, one or more of the contacting ends may have an irregular cross-sectional shape.
In yet another aspect, the present invention relates to an apparatus of the type described above in which the non-contacting end of at least one of the light fibers has a circular cross-section.
In some embodiments of the invention described above, the non-contacting end of at least one of the light fibers has a cross-sectional shape corresponding to the prescribed cross-sectional shape of its contacting end. In other cases, the non-contacting end of at least one of the light fibers has a cross-sectional shape different from the prescribed cross-sectional shape of the contacting end. If the contacting and non-contacting ends of at least one light fiber differ in shape, the light fiber undergoes a transition from the cross-sectional shape of its contacting end to the cross-sectional shape of its non-contacting end. The transition occurs over a predetermined portion of the length of the light fiber, which in some cases may be the entire length of the fiber.
In another aspect, the present invention relates to a method for transporting light from a single source to multiple prescribed locations. In accordance with the method, light is directed into a light injection plane formed by a plurality of light fiber input ends. The input ends of each light fiber have a prescribed cross-sectional shape selected such that adjacent input ends have outer peripheries contiguous with one another so that the light injection plane is substantially free of voids or other non-light-guiding materials. The output ends of the light fibers are then oriented so that light emitted therefrom is applied to the respective prescribed locations.
In yet another aspect, the present invention relates to a method for making a light transport device. In accordance with the method, a plurality of light fibers is provided, each having a contacting end and a non-contacting end. The contacting ends of the light fibers have prescribed cross-sectional shapes prior to being brought into contact with one another. The prescribed cross-sectional shapes are selected such that when the outer edges of the contacting ends are brought together in a given orientation, they will contact one another in a completely contiguous manner. Finally, the contacting ends are arranged in a bundled region that is configured so that light propagating in each of the light guides undergoes mixing by being coupled from one light guide to another. The light fibers employed in this or other embodiments of the present invention may be advantageously fabricated using a molding process.